1. Field of the Invention
This invention relates to a new process for the production of polyisocyanates containing isocyanurate groups by partial trimerization of the isocyanate groups of organic polyisocyanates with the (simultaneous) use of certain alkyl-substituted phenylene diisocyanates as starting polyisocyanate. This invention also relates to the compounds which may be obtained according to this process and to the use thereof for the production of isocyanate-polyaddition products such as polyurethanes.
2. Description of the Prior Art
A large number of processes for the production of polyisocyanates containing isocyanurate groups are known (J. H. Saunders and K. C. Frisch, Polyurethanes Chemistry and Technology, Part I, P. 94 et seq [1962]). In these processes, trimerization catalysts of the most varied type, stated by way of example in the above-mentioned reference, are used. In addition to the trimerization catalysts which are disclosed by way of example in the above-mentioned reference, the following have more recently proved to be universally usable trimerization catalysts: in particular Mannich bases (DE-OS No. 2,551,634 or DE-OS No. 2,641,380) for the trimerization of aromatic isocyanates, quaternary hydroxyalkyl ammonium hydroxides (EP-PS No. 37 65, U.S. Pat. No. 4,288,586, EP-PS No. 10 589 or U.S. Pat. No. 4,324,879) for the trimerization of aliphatic or cycloaliphatic polyisocyanates or complexed basic sodium or potassium compounds (DE-OS No. 3,100,262 or DE-OS No. 3,100,263). The processes and catalysts described in DE-OS No. 2,616,415 and DE-OS No. 2,616,416 are also very suitable.
An important area of use for the previously known polyisocyanates containing isocyanurate groups is the use thereof as reaction components in two-component polyurethane lacquers in combination with reaction components containing hydroxyl groups, for example combined with polyhydroxy-polyacrylates, polyhydroxypolyesters or alkyd resins containing hydroxyl groups.
However, most known polyisocyanates which contain isocyanurate groups still suffer from a number of disadvantages which are worth improving. Thus, the prior art polyisocyanates containing isocyanurate groups can only be diluted with difficulty using non-polar lacquer solvents, for example aliphatic or aromatic hydrocarbons. This disadvantage is manifested by the fact that when the polyisocyanates containing isocyanurate groups are mixed with aliphatic or aromatic hydrocarbons or with polyesters, polyacrylates or alkyd resins which are dissolved in these solvents, cloudiness and precipitation occur which render the production of lacquers impossible.
Another disadvantage of the prior art polyisocyanates containing isocyanurate groups is to be attributed to the frequently occurring incompatibility thereof with other binders and reaction components, which is manifested in a frequently too short processing time of the ready-for-use lacquer mixtures. The reason for this frequently too short processing time is attributed in particular to the fact that with the formation of only a few urethane groups in the ready-for-use lacquers, the solubility or compatibility which is poor anyhow becomes even poorer and the binder precipitates from the lacquer solution. The obvious idea of overcoming the poor compatibility by the simultaneous use of polar solvents results in a considerable increase in the price of the lacquers. The modification of the polyisocyanates with fatty alcohols which is recommended in DE-AS No. 2,414,413 implies a substantial improvement, but it has the disadvantage that due to this modification, isocyanate groups are used up which are no longer available for the formation of cross-linking points and which reduce the functionality of the polyisocyanates.
Therefore, an object of the present invention is to provide new, easily accessible polyisocyanates which contain isocyanurate groups; are compatible with slightly polar solvents and diluents; are miscible with hydroxyl-polyesters, hydroxyl-polyacrylates and hydroxylalkyd resins without clouding, even in the presence of non-polar solvents; and which have an improved processing time in admixture with these reaction components.
This object may be achieved by the process according to the present invention which is described in more detail in the following.